1. Field of the Invention
The present invention relates to isolation mechanisms for electrically isolating control input mechanisms of boomed apparatuses. More particularly, the present invention concerns an isolation mechanism for electrically isolating a control input mechanism of an otherwise substantially conventional boomed apparatus, such as, for example, an aerial device, digger derrick, or crane, having a workstation coupled with a movable boom, wherein the isolation mechanism allows a worker to control movement of the boom and positioning of the work station while protecting against electrical discharge along substantially any path which includes the control input mechanism.
2. Description of the Prior Art
It is often desirable, particularly in the electric utility industry, to provide a boomed apparatus, such as, for example, an aerial device, digger derrick, or crane, operable to facilitate work at or from an elevated position. Such a boomed apparatus is embodied in, for example, a common bucket truck operable to facilitate work high on an electric utility pole or on a wall of a building.
Typically, a bucket truck broadly comprises a work station; a movable boom; a vehicular platform; a control input mechanism; and a control assembly. The work station is operable to lift or otherwise carry at least one worker to the elevated work site, and is coupled with the boom at or near a distal end thereof. Because the work station may be used near highly-charged electrical lines or devices, the work station must be electrically isolated so as to prevent damaging electrical discharge or electrocution of the worker. Thus, the work station is commonly provided with a protective, non-conductive liner so that the worker, as long as he or she remains completely inside the work station and liner, is protected from electrocution.
The boom is movable so as to elevate and otherwise position the work station where desired, and is coupled with the vehicular platform at or near a base end of the boom which is substantially opposite the distal end. Commonly, in order to further electrically isolate the work station from electrical discharge via the boom and the vehicular platform, an intermediate portion or section of the boom is constructed of or covered with an electrically non-conductive, or dielectric, material. The distal end of the boom, however, though electrically isolated from the vehicular platform, must incorporate structural material so as to have sufficient structural strength to support the work station and worker. This structural material is typically an electrically conductive metal, such as steel, with the work station and control assembly being directly exposed or dangerously close thereto.
The vehicular platform is motorized and wheeled or otherwise adapted to quickly and efficiently travel to and from the work site. The vehicular platform will either be in direct contact with an electrical ground, such as, for example, the Earth, or imminently at risk of direct or indirect contact therewith.
The control input mechanism allows the elevated worker to provide a control input to control, via the control assembly, movement of the boom and positioning of the work station. Commonly, the control assembly comprises one or more hydraulic control valves, one or more fluid conduits and a quantity of hydraulic fluid, to transmit the control input down the boom for implementation. The necessary conduit connections, however, prevent the control valves from being located inside the work station and its protective liner. Furthermore, as the control input mechanism must be in direct physical contact with the control assembly in order to actuate the valves in accordance with the control input, the control input mechanism must also be located outside the work station and protective liner. Thus, the worker must reach outside the protective liner to actuate the control input mechanism, thereby exposing him or herself to electrocution. This is of particular concern given that the control valves to which the control input mechanism is coupled are typically constructed of an electrically conductive material. Furthermore, the control valves may be located in close proximity to the aforementioned electrically conductive structural support material used to reinforce the distal end of the boom.
Thus, although the aforementioned dielectric boom portion does protect against electrical discharge via the boom and vehicular platform, it does not protect against direct discharge via the electrically conductive structural material in the distal end of the boom, via the control valves, and via the control input mechanism, thereby leaving the worker vulnerable to damaging or deadly phase-to-phase or phase-to-ground electrical discharge along these paths. For example, were the work station or distal end of the boom to move into or otherwise come into contact with a first phase or ground conductor while the worker is in contact with the control input mechanism and second conductor, the worker would be electrocuted. In this case, the discharge path is from the first conductor, to the distal end of the boom, to the control input mechanism, to the worker, and to the second conductor. It will be appreciated that the dielectric boom portion provides no protection against this or similar discharge paths.
Due to the aforementioned problems and disadvantages in the prior art, a need exists for an improved isolation mechanism for protecting the worker against electrical discharge along substantially any path which includes the control input mechanism.